Grid computing is concerned with the sharing and coordinated use of diverse resources in dynamic, distributed \"virtual organizations.\" The dynamic nature of Grid environments introduces challenging security concerns that demand new technical approaches. In this brief overview, we review key Grid security issues and outline the technologies that are being developed to address those issues. We focus in particular on work being done within the context of the Open Grid Services Architecture, a new initiative aimed at recasting key Grid concepts within a service-oriented framework. This work involves a tight integration with Web services mechanisms and appears particularly relevant to the concerns of e-services.